Welcome to visit Geoscience!

Geoscience ›› 2018, Vol. 32 ›› Issue (01): 28-44.DOI: 10.19657/j.geoscience.1000-8527.2018.01.03

• Petrology • Previous Articles     Next Articles

Characteristics of Chronology and Geochemistry for the Cenozoic Alkali-rich Porphyry in Lijiang Area, Western Yunnan and Their Significance

HUANG Yonggao(), LUO Gai, ZHANG Tong, XIONG Changli, JIA Xiaochuan, YANG Xuejun   

  1. Sichuan Institute of Geological Survey, Chengdu, Sichuan 610081, China
  • Received:2017-04-28 Revised:2017-10-30 Online:2018-02-10 Published:2018-02-05

Abstract:

The Cenozoic alkali-rich porphyry in Lijiang region of Western Yunnan is located in the connection part between Sanjiang fold orogenic belt and southwest of Yangtze plate, including alkali rock and alkali-granite. Alkali rock includes orthophyre, syenite and trachyte-prophyry, while alkali granite includes granite-prophyry, monzonitic granite-prophyry and masanophyre. The zircon U-Pb dating indicates that the ages of those porphyry are between 34.6 and 37.1 Ma, which is consistent with the ages of Cenozoic alkali-rich porphyry in Western Yunnan. Geochemical results showed that alkali rock belongs shoshonite series, with SiO2 content of 54.54%-67.70%, K2O>Na2O. Alkali-granite belongs high-K calc-alkalic series, with SiO2 content of 67.16%-70.66%, K2O<Na2O. They are both enriched in alkali (Na2O+K2O=7.03%-11.70%), showing metaluminous and weak peraluminous (A/CNK=0.64-1.15) characteristics. The porphyry shows alkali and adakitic geochemical characteristics, with enrichment of LREE and LILE(Sr, Ba, K, Pb, and so on), deficit of HREE and HFSE(Nb, Ta, Ti, and so on), with high Sr content and ratio of Sr/Y, La/Yb, low Y and Yb contents, and low values of Mg# (<0.5). The comprehensive study shows that the porphyry is associated with partial melting of the base of thickened lower crust caused by decompression melting and underplating of mantle-derived magmas, formed from the structure transition phase of late-collisional between Indian and Asian continents, and was the magmatic event response to syn-collisional processes in the structural transform zone of southeast of the Tibetan orogen. It is considered that there is great gold-polymetallic prospective reserves of porphyry-hydrothermal deposits. This paper provides important constraints for understanding deeply the tectonic-magmatic-metallogenic processes of the Lijiang porphyry metallogenetic belt.

Key words: Cenozoic alkali-rich porphyry, zircon U-Pb geochronology, geochemistry, Lijiang area, Western Yunnan

CLC Number: